1. Field of Invention
The present invention relates to a process using radiofrequency microwave energy to catalyze chemical reactions within a liquid film internal to the waveguide transmitting said energy.
2. Background
A liquid medium is a common place for chemical reactions since said liquid can represent a solution or mixture. Water solubility of inorganic chemicals is particularly common; however, the liquid medium is not restricted to water. When such chemical liquids are organic in nature, reactions between the liquid mixture constituents often occur slowly; thus, enhancement of such chemical reaction rates is often desirable. The subject invention positions this liquid as a thin film within an operating radiofrequency energy waveguide. The microwave energy thus catalyzes the desired chemical reactions.
Quantum radiofrequency (RF) physics is based upon the phenomenon of resonant interaction with matter of electromagnetic radiation in the microwave and RF regions since every atom or molecule can absorb, and thus radiate, electromagnetic waves of various wavelengths. The rotational and vibrational frequencies of the electrons represent the most important frequency range. The electromagnetic frequency spectrum is conveniently divided into ultrasonic, microwave, and optical regions. The microwave region runs from 300 Mhz (megahertz) to 300 Ghz (gigahertz) and encompasses frequencies used for much communication equipment. For additional information refer to N. Cook, Microwave Principles and Systems, Prentice-Hall, 1986.
Often the term microwaves or microwave energy is applied to a broad range of radiofrequency energies particularly with respect to the common heating frequencies, 915 MHz and 2450 MHz. The former is often employed in industrial nearing applications while the latter is the frequency of the common household microwave oven and therefore represents a good frequency to excite water molecules, in this writing the term `microwaves` is generally employed to represent `radiofrequency energies selected from the range of about 915 to 5000 MHz`, since in a practical sense this total range is employable for the subdue invention.
The absorption of microwaves by the energy bands, particularly the vibrational energy levels, of the atoms or molecules results in the thermal activation of the nonplasma material and the excitation of valence electrons. The nonplasma nature of these interactions is important for a separate and distinct form of heating employs plasma formed by arc conditions of a high temperature, often more than 3000.degree. F., and at much reduced pressures or vacuum conditions. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Supplementary Volume, pages 599-608, Plasma Technology. In microwave technology, as applied in the subject invention, neither condition is present and therefore no plasmas are formed.
These microwaves lower the effective activation energy required for desirable chemical reactions since they can act locally on a microscopic scale by exciting electrons of a specific atom in contrast to normal global heating by raising the bulk temperature. Further this microscopic interaction is favored by polar molecules whose electrons become locally excited leading to high chemical activity; however, nonpolar molecules adjacent to such polar molecules are affected to a much lesser extent. An example is the heating of polar water molecules in a common household microwave oven where the container is of nonpolar material that is microwave-passing and stays relatively cool.
A polar material interacts with microwaves readily and rapidly degrades its effective penetrating power. This aspect is employed in waveguides for microwave transmission since the waveguide transmits the energy along the skin of the guide; therefore, the guide is hollow. Such a hollow waveguide, often called a waveguide cavity, contains a substantially uniform energy field that is utilized in the subject invention to interact with a liquid film. This film of liquid if of a polar nature, like water, will quickly degrade the microwave energy and is referred to as microwave-absorbing; thus, only a thin surface layer is effective. The concept of penetration depth Is often employed to indicate the distance into a medium that is penetrated by a given frequency of radiofrequency energy. For water using 2450 MHz microwaves this penetration depth is approximately one to two centimeters.
It is common to refer to a thin film, or if appropriate thin liquid film, for such microwaves interaction. In microwave catalysis the best results occur when the polar molecules of the thin film represent a chemical reactant.
When the thin liquid film is potentially nonpolar, such as a symmetric organic molecule, and thus largely microwave-passing, most local microwaves interaction occurs with polar constituents dissolved or carried by said film. Thus first order chemical reactions, such as chemical decompositions, are the easiest to microwave catalyze.
As used above microwaves are often referred to as a form of catalysis when applied to chemical reaction rates. See Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
Related U.S. patents using microwaves include:
______________________________________ U.S. Pat. No. Inventor Year ______________________________________ 4,076,606 Suzuki et al. 1978 4,345,983 Wan 1982 4,545,879 Wan et al 1985 ______________________________________
Referring to the above list, Suzuki discloses a process for homogeneously decomposing nitrogen dioxide using microwave irradiation at the standard microwave frequency in an exhaust gas stream. Wan discloses a method for decomposing solid chlorinated hydrocarbons with a ferromagnetic catalyst using microwave heating. Wan et al disclose employing microwave heating to desulphurize pulverized petroleum pitch using a ferromagnetic catalyst.